1. Field of the Invention
The present invention is generally related to an engine control method for a marine propulsion system and, more specifically, to a method that controls the deceleration of an engine in a manner that improves the steering capability of a marine vessel.
2. Description of the Prior Art
Certain types of marine vessels use jet pumps, or water jets, with impellers as their primary marine propulsion system. For example, jet boats and personal watercraft use an internal combustion engine that rotates an impeller of a jet pump, in order to draw water from a body of water and expel the water rearwardly through a nozzle in order to provide propulsion for the marine vessel.
Certain jet pump propulsion systems are combined with a rudder or steering tabs which project downwardly from the marine vessel to assist in steering. However, these steering fins or rudders are generally undesirable because they are easily damaged if they strike submerged objects. In addition, steering fins or rudders can damage marine life or harm swimmers.
If the marine propulsion system is not provided with a steering fin or rudder, the water jet propulsion system can experience seriously reduced steering control when the throttle is rapidly reduced to idle speed because the steering capability of a water jet propulsion system is highly dependent on the magnitude of water flowing through the jet pump and its steering nozzle.
To improve this problem, certain manufacturers of jet pump marine propulsion systems utilize abnormally high engine idle speeds. In some cases, these higher idle speeds are permanently fixed at a magnitude which is greater than 20% of the maximum operating speed of the engine. This approach to a solution of the steering problem has numerous drawbacks, including potential movement of the watercraft even while in neutral, increased sand and debris ingestion by the impeller when in neutral, and possible difficulty in shifting from neutral to forward gear. Additionally, a high idle speed can waste a significant amount of fuel.
Some manufacturers of personal watercraft or jet boats introduce a throttle advance mechanism that is mechanically connected to the steering wheel. When the steering wheel is turned to a full right or full left position, the engine speed is increased to a magnitude that is approximately 150% to 170% of normal idle speed. While this technique improves the steering capability at low speeds, it can be troublesome when an operator attempts to maneuver the marine vessel at slow speeds.
U.S. Pat. No. 4,031,844, which issued to Onal et al on Jun. 28, 1977, describes a dual jet boat pump. A double suction, double volute pump for propelling a boat having each volute exhaust through a separate jet nozzle is described. The pump housing defines two intake passageways leading upward to either side of a double suction impeller. The housing further provides double volutes which receive water from each side of the double suction impeller and deliver it to dual nozzles thereby creating twin jets which may be employed to propel and control the boat. The double volutes each extend substantially full circle about the housing and terminate in elbows which lead to the nozzles. The nozzles are placed horizontally equidistant from the center line of the impeller shaft and are controlled by steering linkages to operate in unison. Reversing control gates may be operated either together for reversing or independently for slow speed steering.
U.S. Pat. No. 5,755,601 which issued to Jones on May 26, 1998, describes a brake system for a personal watercraft. A jet propelled watercraft has a brake which the driver of the watercraft can use to decelerate forward motion of the watercraft. The brake mechanism preferably includes a reverse gate which allows the watercraft steering to be consistent when the watercraft is accelerating or cruising with the reverse gate in full up position as when the watercraft is decelerating with the reverse gate in a full down or partially down position. The positioning of the reverse gate during operation of the watercraft is adjusted in accordance with the state of hand operated actuators for a forward throttle control mechanism and a brake control mechanism. Preferably, an electronic controller receives a signal from the control mechanisms and outputs a control signal that directs a servo motor to move a reverse gate cable or linkage to position the reverse gate. Forward thrust can be increased by proportionally closing the actuator for the forward thrust control mechanism. In addition, reverse thrust or braking thrust can be increased by proportionally closing the actuator for the brake control mechanism.
U.S. Pat. No. 5,813,357, which issued to Watson on Sep. 29, 1998, describes a jet ski steering and braking system. The system for steering and braking a jet ski watercraft uses flaps that may be independently or uniformly extended from a forward area of the watercraft hull. The flaps are located at or below the water line during operation.
U.S. Pat. No. 5,193,478, which issued to Mardikian on Mar. 16, 1993, describes an adjustable brake and control flap system for a watercraft. The system is used for trimming, steering, and braking a watercraft and includes a retractable plate or flap disposed on each lateral side of the hull of the watercraft. Each flap is extendible into the water, rearwardly in a continuously adjustable manner, and independently of the extension of the other flap. When the flap is fully extended, its angular position relative to the hull is also continuously adjustable independently of the angular positioning of the other flap. The flaps in their fully declined position act as powerful brakes for the watercraft. Differential extension of the flaps or differential adjustment of their relative angular positions on the two sides of the watercraft results in trimming and steering of the watercraft.
U.S. Pat. No. 5,476,401, which issued to Peterson et al on Dec. 19, 1995, describes a compact water jet propulsion system for a marine vehicle. The device provides an improved water jet propulsion system for a marine vehicle. The water jet propulsion system incorporates an unconventional and compact design including a short, steep, hydrodynamically designed inlet duct adapted for mounting to the surface of the vehicle hull and extending internally thereof, a water jet pump having an inlet end attached to the outlet end of the inlet duct, a motor for rotating the pump impeller, a driveshaft located completely outside of the flow path connecting the motor with the pump impeller, a flow passage for discharging accelerated flow received from the pump in a generally rearward direction, and a steering and reversing mechanism pivotally mounted about a substantially vertical axis to the aft portion of the vehicle hull for redirect accelerated flow received from the outlet nozzle so as to provide maneuvering capability to the vehicle.
U.S. Pat. No. 5,894,087, which issued to Ohtuka et al on Apr. 13, 1999, describes a speed sensor for a watercraft. The arrangement of a speed sensor on a personal watercraft shields the sensor from damage while simplifying the layout and arrangement of the sensor on the underside of the watercraft hull. The hull includes a pump chamber formed in part by a front wall. The speed sensor is attached to the wall with a portion of the sensor projecting below a housing of the sensor. A ride plate covers a lower opening of the pump chamber and fits about the sensor housing. In this location, the speed sensor does not interfere with the arrangement or operation of steering or trim mechanism used with a jet propulsion unit housed within the pump chamber. The speed sensor also is generally protected in this location and is not visible from the rear of the watercraft to improve the watercraft""s aesthetics.
The patents described above are hereby explicitly incorporated by reference in the description of the present invention.
The present invention, in a particularly preferred embodiment, provides a method for controlling an engine of a marine propulsion system of a marine vessel. The method comprises the steps of monitoring an engine speed command signal. The engine speed command signal can be representative of a manually operated throttle control. The method further comprises the steps of determining a speed of the marine vessel and causing a speed of the engine to decelerate less than a speed indicated by the engine speed command signal when the engine speed command signal indicates a command for deceleration to a commanded speed, such as idle speed, which is less than a first preselected threshold. For example, if a marine propulsion system is being operated at a certain engine speed, and the marine vessel is moving at planing speed, and a manual engine speed command signal is received to quickly reduce the engine speed, the method of the present invention responds to that manual signal by decelerating the engine speed at a lesser rate or to an engine speed which is more than the indicated desired engine speed if the manually controlled engine speed command signal indicates a desired engine speed which is less than a first preselected threshold, typically equivalent to a speed slightly greater than an idle speed magnitude.
The causing step can apply a rate of deceleration that is generally equal to that which is indicated by the engine speed command signal, but limits the magnitude of decrease in engine speed to a result that is greater than the commanded engine speed. For example, if the manually controlled speed command signal indicates a desire to reduce the speed to idle speed, the causing step can reduce the speed at the normal deceleration rate, but to a minimum magnitude greater than idle speed. Alternatively, the causing step can apply a rate of deceleration which is less than that which is indicated by the engine speed command signal. In other words, if the manually controlled engine speed command signal indicates that the engine speed should be quickly reduced from its current operating speed to its idle speed in less than one second, for example, the rate of deceleration may be slowed to reduce the speed to idle speed in three or more seconds. With these two alternative embodiments, either the final reduced speed magnitude can be affected or the rate at which the commanded final speed magnitude is achieved can be affected. In both cases, the overall time duration from the occurrence of the speed command signal to the achievement of minimum speed is increased to maintain a longer period of improved steering control for the operator of the marine vessel.
In certain embodiments of the present invention, the causing step is only performed if the speed of the engine is greater than a second preselected threshold, such as planing speed, when the speed reduction command is received. The speed of the vessel can either be measured directly by a speedometer or indirectly as a function of engine speed and operating conditions. In certain embodiments of the present invention, the causing step can decrease the speed of the engine as a step function from an engine speed magnitude when the engine speed command signal initially indicates a command for deceleration to an engine speed which is generally equal to the engine speed command signal. This step function can comprise one or more individual and discrete steps. The marine propulsion system can comprise a jet pump and can be incorporated within a personal watercraft or a jet boat.